The long-term objective of the proposed research is to elucidate the regulatory interactions of all the macromolecules involved in the virus assembly process. We have chosen the phi chi-174 system because physiology and genetics of the process of the phage assembly in vivo have been well characterized. We have set the following sequence as the most effective way to implement our research: (1) to establish a virus assembly pathway map that represents the processes occurring in the infected cells; (2) to develop an in vitro system that will mimic the in vivo situation and will synthesize biologically active viruses; (3) to identify all of the virus-coded proteins as well as the host-originated proteins that are needed for infectious virus synthesis and; (4) to elucidate the regulatory interactions of the macromolecules involved in the virus assembly processes. Based on a number of in vivo observations we are now able to propose a working hypothesis on the functions of most of the phage-coded genes. We have also developed an in vitro system which synthesizes infectious phage particles. The system is composed of purified phage coded proteins and uninfected host extract. These two systems will provide a complementary approach to each other in order to achieve the long-term objective. We hope that phi chi-174 system will provide a model system for the maturation processes of the other spherical viruses including animal and plant viruses.